1. Field of the Invention
The present invention relates to an image stabilization apparatus to be equipped in various optical apparatus such as a binocular or monocular.
2. Related Background Art
Reference is made here, by way of example, to Japanese Patent Application Laid-Open No. 10-104681, which discloses an image stabilization apparatus. A prior art image stabilization apparatus disclosed in this Japanese Patent Application Laid-Open No. 10-104681 is provided with an erecting prism, a gimbaled member to which the erecting prism is attached, position feedback control means and angular velocity feedback control means for controlling the position or posture of the gimbaled member. The angular velocity feedback control means is a feedback loop that detects an angular velocity of the gimbaled member that is created due to hand shake or other causes and enhances following-up ability of the gimbaled member to the optical axis of the objective lens based on a detection result. A position feedback loop is a feedback loop that detects an angular displacement of the gimbaled member that is created due to hand shake or other causes and enhances following-up ability of the gimbaled member to the optical axis of the objective lens based on a detection result. With the above-described structure, Japanese Patent Application Laid-open No. 10-104681 teaches a technology to change a gain of the position feedback control means in response to a user's switching operation of a mode switch to realize a mode for reducing vibration created by hand shake and a mode for providing a high following-up performance to panning and tilting operations.
Another patent document Japanese Patent Application Laid-Open No. 2001-100106 discloses an image stabilization apparatus in which a vibration reduction mode and a panning/tilting mode are switched automatically.
Specifically, in this prior art, the apparatus detects the angular velocity and an angular positional displacement of a gimbaled member and determines whether or not the detected values are larger (or alternatively, smaller) than predetermined values. Then, the apparatus determines an appropriate mode to automatically set this appropriate mode.
In addition, in the technology disclosed in Japanese Patent Application Laid-Open No. 2001-100106, a user can freely switch the mode at his or her will by a manual operation. Even during observation under a mode that has been set manually, the apparatus detects the angular velocity and the angular positional displacement of the gimbaled member, determines the appropriate mode, and when it is determined that the appropriate mode is different from the manually selected mode, the mode is automatically switched to the appropriate mode determined by the apparatus.
In the above-described technology disclosed in Japanese Patent Application Laid-Open No. 10-104681, the mode is manually selected on user's own discretion, and therefore it would be difficult for an unskilled user to determine the optimum mode definitely. Therefore, in some cases, a mode other than that selected by the user may be the optimum mode. In such cases, the performance of the apparatus would not be brought out fully.
On the other hand, in the technology disclosed in Japanese Patent Application Laid-Open No. 2001-100106, the switching of the vibration reduction mode is effected automatically in accordance with the degree of the vibration of the apparatus. However, if the mode is thus switched automatically, the mode determined by the apparatus as the appropriate mode sometimes differs from the mode that the user has selected in accordance with his or her intention. In that case, the user sometimes feels it undesirable to observe under the mode automatically switched based on the determination by the apparatus.